Lithography techniques and methods, such as, for example, photolithography, imprint lithography, nanoimprint lithography, and contact lithography may be used to fabricate structures that include features having microscale (i.e., less than about 100 microns) or nanoscale (i.e., less than about 100 nanometers) dimensions. Such structures include, for example, integrated circuits, sensors, light-emitting diodes, and nanostructures. In lithographic techniques, multi-layer structures are fabricated in a layer-by-layer process.
Briefly, in photolithography, a layer of photoresist is provided over a substrate, and a selectively patterned mask or reticle is aligned over the layer of photoresist. Selected areas of the layer of photoresist material may be exposed to electromagnetic radiation through the patterned mask or reticle, which may cause a chemical and/or physical transformation in the selected areas of the layer of photoresist material. In a subsequent development step, either the selected areas of the layer of photoresist material that have been exposed to the electromagnetic radiation or the other areas of the layer of photoresist material that have been shielded from the electromagnetic radiation by the mask or reticle are removed from the underlying substrate. In this manner, the selected pattern in the mask or reticle may be positively or negatively transferred to the layer of photoresist material.
The underlying substrate then may be further processed (e.g., material may be removed, deposited, doped, etc.) through the patterned layer of photoresist material, thereby forming a selectively patterned layer (corresponding to the selectively patterned mask or reticle) in or on the underlying substrate. Additional selectively patterned layers then may be formed over the previously formed selectively patterned layer using additional masks or reticles as necessary.
In order to position each layer relative to the underlying layers, the substrate and the masks or reticles typically are marked with an alignment feature or mark. As each mask or reticle is positioned over the underlying substrate, the alignment feature on the mask or reticle may be aligned with the alignment feature on the substrate before exposing the layer of photoresist material to electromagnetic radiation through the mask or reticle.
In imprint lithography (including nanoimprint lithography), a layer of deformable material (such as, for example, uncured methylmethacrylate (MMA)) may be provided over a substrate. A selectively patterned surface of an imprint mold then may be aligned over the layer of deformable material and pressed into the layer of deformable material, thereby transferring the pattern in the selectively patterned surface of the imprint mold to the layer of deformable material. The deformable material may be cured to solidify the pattern formed in the layer of deformable material. The pattern formed in the layer of deformable material may include a plurality of relatively thicker regions and relatively thinner regions in the layer of deformable material.
At least a portion of the patterned layer of deformable material then may be etched or otherwise removed until the relatively thinner regions in the patterned layer of deformable material have been substantially removed, the remaining portions of the relatively thicker regions in the layer of deformable material forming a pattern over the underlying substrate. In this manner, the selected pattern in the imprint mold may be transferred to the layer of deformable material.
The underlying substrate then may be further processed (e.g., material may be removed, deposited, doped, etc.) through the patterned layer of deformable material, thereby forming a selectively patterned layer (corresponding to the selectively patterned imprint mold) in or on the underlying substrate. Additional selectively patterned layers then may be formed over the previously formed selectively patterned layer using additional imprint molds as necessary.
As in photolithography, in order to position each layer relative to the underlying layers, the substrate and the imprint molds typically are marked with an alignment feature or mark. As each imprint mold is positioned over the underlying substrate, the alignment feature on the imprint mold is aligned with the alignment feature on the substrate before pressing the imprint mold into the layer of deformable material on the surface of the underlying substrate.
In all lithography processes, it may be important to ensure that each layer formed or processed is accurately aligned with layers that have been previously formed or processed and layers to be subsequently formed or processed.